One aspect of the mission of the NICHD is to support basic research in human development. The Language, Literacy and Bilingualism program supports research into the mechanisms underlying typical language development and language related processes. The research proposed here will ask how children might use information available in the speech that they hear to learn that a word has more than one meaning. Such homonyms are common in speech to and by children and yet most theories of word learning do not include an account of how they are learned. These studies will begin by examining the speech that children hear in their everyday experience and measuring the acoustic properties of homonyms. Prior work indicates that apparent homonyms are not perceptually identical, but rather that they differ in their acoustic properties depending on which meaning is intended by the speaker. This research will also examine whether children produce the same kinds of distinctions in their own use of homonyms. If such information is available, do children use it to process and learn words? To test this, the proposed research will examine whether children and adults perceive these differences in fluent speech, as well as in isolated instances of words. First, adults and children will be asked to rate the naturalness of sentences that have had the target word replaced with a homonym. This will show that they are sensitive to differences in homonym pronunciation when they are processing sentences. Then, adults and children will participate in a priming study, which will test whether a homonym increases processing speed for words related to both of its meanings or just those related to the meaning in which it was used. Finally, this research will use a word learning task with preschool-aged children to determine whether children can use perceptual differences in words to learn a new meaning for a known word, a feat that is known to be problematic for young children. These studies support the mission of the NICHD by providing insight into processes of typical child development. The learning of homonyms may also have important implications for early literacy, as the need to map multiple meanings on to a single form also arises in the domain of reading.